This is a library that creates a software I2C bus on any two pins.
More than one software I2C bus can be created.
It can be installed via the arduino library manager or manually by copying the files to your sketchbook\libraries folder.
The SoftwareWire is only I2C Master mode.
The clock pulse stretching is implemented, so the Slave can be another Arduino board.
See the Small_example.ino how to use it. Include the library, and create a SoftwareWire object with the sda and scl pin. After that is should be just like the real Wire library.

Ver 1.6.0

• Remove virtual on destructor - by @bxparks
• Remove inheritance from TwoWire - by @bxparks
• Remove including Wire.h - by @bxparks

Ver 1.5.1

• Inherit from TwoWire - by @mhenman
• Repeated start fix - by @MortezaAghazamani

Ver 1.5.0

• Added empty constructor
• Updated printStatus() - by @bperrybap
• Removed I2C Slave functions and added error message - by @bperrybap

Ver 1.4.1

• GPLv3 licence

Ver 1.4.0

• i2c_stop is safer with extra delay, and both SDA and SCL are first set low.
• Thanks to Arduino.cc user fjuedes for testing.

Ver 1.3.2

• Added library.properties file

Ver 1.3.1

• Comment added

Ver 1.3.0

• "SoftwareWire" release

Ver 1.2.0

• Added keywords.txt - by @Leo72

Ver 1.1.0

• Selectable I2C speed (30Hz-140kHz)

Ver 1.0.0

• ST7032i LCD driver compatibility
• Bitbanged waveform modified to strictly adhere to I2C standard
• Changed default speed to 100kHz

I was asking for such a library here : http://forum.arduino.cc/index.php?topic=315898
Testato was working on such a library here : http://forum.arduino.cc/index.php?topic=287008
I added some glue to that code to make it behave like the Wire library.
This library started in 2008, and is now the result of the work of four.
Enjoy.
// 2008, Raul wrote a I2C with bit banging as an exercise.
// http://codinglab.blogspot.nl/2008/10/i2c-on-avr-using-bit-banging.html
//
// 2010-2012, Tod E. Kurt takes some tricks from Raul and wrote the SoftI2CMaster library for the Arduino environment.
// https://github.com/todbot/SoftI2CMaster
// http://todbot.com/blog/
//
// 2014-2015, Testato updates the SoftI2CMaster library to make it faster and to make it compatible with the Arduino 1.x API
// Also changed I2C waveform and added speed selection.
//
// 2015, Peter_n renames the library into "SoftwareWire", and made it a drop-in replacement for the Wire library.